SENSORLESS FIELD ORIENTED CONTROL OF BRUSHLESS ...

Figure 2.20 – Elementary brushless PM motors with concentrated full-pitch winding.
The rotor magnets produce airgap flux densities as shown in Figure 2.21. The motor on the left
has magnets that produce an airgap flux density that is a sinusoidal function of the angle around
the rotor, α. The motor on the right has magnets that produce an airgap flux density that is also a
function of the angle around the rotor but whose shape is difficult to describe. However, it has the
notable feature that the magnitude is constant over an angular pitch of β≥120°; note that β has
correspondence between Figure 2.20 and Figure 2.21. If these segments are centered about α=0°
and α=180°, the airgap flux density could be approximated by the trapezoid shown in dashed
lines. These two elementary models are representative of the two most common types of non-
salient BPMS motors (real motors are not always constructed as shown). The motor on the left is
a sinusoidal motor and the motor on the right is an arbitrary trapezoidal motor.
Figure 2.21 – Airgap flux density profiles for two BPMS motors.
The airgap flux densities shown in Figure 2.21 are defined in terms of the angle α around the
rotor. But since the coilsides that compose the winding have fixed positions it is possible to
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